Caps may be of any one of a number of different kinds. For example, they may be of the familiar type which is removed from the container by twisting the cap through part of one turn so as to release a plurality of locking projections of the cap from corresponding retaining means formed about the mouth of the container. These caps can be referred to as "twist-off caps", as distinct from another type which is the screw cap. A screw cap has to be unscrewed in order to remove it from the container, (usually by at least one full revolution of rotation), and most screw caps are applied to the containers by screwing them on to the latter by rotation through the same number of revolutions in the opposite direction. Twist-off caps may be applied by similar reverse rotation; but they may alternatively be adapted to be secured to the containers by applying to the cap a simple axial force which pushes the cap into position, the cap or the container or both (but usually the cap) having suitable resilience to allow the locking projection or projections to be deformed during this operation and to spring into their locking condition when the cap is fully home on the container. Such a cap may be referred to as a "push-on, twist-off" cap.
A further kind of cap which is secured to the container by application of a simple axial force is that of the so-called "pry-off" type which is removed by upward leverage so that it springs off the container without any rotational movement.
The invention is particularly concerned with capping machines capable of applying, at high speed, a succession of caps to a succession of respective containers, the caps being for example of any of the kinds discussed above. Such machines are to be found in the filling plants of manufacturers of products such as foodstuffs, beverages and other flowable substances. In the case of many products it is required that the product be vacuum packed, i.e. the filled container, as yet uncapped, is passed into an enclosure in which the air pressure is lower than the ambient pressure. The cap is secured to the container within this enclosure, so that on emerging from the enclosure, the filled and sealed container contains, above the product therein, a partial vacuum. The term "vacuum", when used herein, is to be understood to mean such a partial vacuum.
There are a number of problems today encountered in connection with the use of high-speed capping machines for capping large quantities of containers. One such problem arises from the fact that successive batches of a product may be required to be packed in containers of different capacities. Thus, for example, one batch may be packed in jars of a particular height, and the next in jars which are of lesser height. Conventionally the jars are passed through the capping machine on a linear conveyor moving horizontally. In order to apply the caps, cap-applying means of the machine are set at the appropriate working height above the conveyor, and consequently have to be re-set to a different working height when the height of the jars is changed. This normally entails the removal of certain parts of the machine and their replacement by "change parts" having different dimensions, in order to achieve the required versatility.
A typical capping machine has a cap-applying or capping head mounted above the conveyor, the capping head being arranged to place a cap upon each container in turn at a feed or pick-up station, and to secure or seal the cap to the container at a subsequent sealing station. To this end the capping head includes a capping head body, carrying a cap chute at the pick-up station and sealing means at the sealing station. Conventionally, the capping head is mounted above the conveyor by means of appropriate vertical supports at both sides of the conveyor. To adjust the vertical position of the capping head above the conveyor (the "head height") it is necessary to provide change parts in the form of these supports of different lengths.
The cap chute must be capable of accurately positioning each cap in turn so that the appropriate container will engage the cap in the correct orientation and centrally. Accordingly the cap chute comprises a pair of guide rails, along which the caps are fed, and which in the pick-up position are separated, transversely of the path of the containers, by an amount approximating to the diameter of the cap so as to hold the latter in its correct position.
The cap chute conventionally has some means for arresting each cap in turn, and for retaining it temporarily, in its pick-up position. Such arresting and retaining means has to be such that, when the cap is engaged by a leading upper portion of the approaching container, the cap can then be advanced past the retaining means without difficulty, and particularly without applying to the cap any force that might lift or jerk it off the container or out of its correct position upon the latter. Numerous arresting and retaining means for this purpose have been proposed in the past, and a number of them have been used successfully in production. Some of these prior art cap chutes involve moving parts, usually spring-loaded; others rely on particular features of the geometry of the fixed cap guide rails of the cap chute, such as a "step" over which the cap is lifted by the container as it comes into engagement therewith (see for example United Kingdom patent specification No. GB-A-1408535). In pursuit of higher operating speeds, however, it becomes desirable to minimise the forces applied to the cap as much as possible; whilst in the interests of reliability and ease of maintenance it is equally desirable to ensure that the components are as simple and accessible as possible.
In one particular form of prior art cap chute, described in United Kingdom patent specification No. GB-A-2040892, the arresting and retaining means of the cap chute comprises a pair of stop pins extending towards each other, transversely of the path of the caps, each stop pin being mounted in a housing formed integrally in a side guide wall of a respective one of the cap guide rails of the chute, and biased into its extended position by a compression spring concealed within the housing. When the cap is engaged by a container, for example by the leading portion of the terminal lip of a glass jar coming into contact with the interior of the leading portion of the cap skirt, the cap is pushed forward by the advancing container so as to force the stop pins to retract against the action of their springs. Not only may some considerable force be required to retract the springs, but the force so applied may result in some cases in "rebound" so that the springs may tend to apply an impulse to the stop pins such as to hit the cap and lift it from the container. In any event, the use of captive compression springs results in the need to stop the capping machine, and to remove and dismantle the whole cap chute, when it becomes necessary to replace the springs, an operation that is required at frequent intervals.
It is of course necessary that the containers be correctly centred with respect to a longitudinal centre plane of their path along the conveyor of the capping machine, and also that they be positively driven along this path. Whilst the moving conveyor does advance the containers mounted on it, and could be provided with dogs or other pushing devices for applying a positive forward driving force to them, there is always a danger of the containers toppling when subjected to forces at their upper ends during the capping operations of placing the cap upon the container, (cap placement), and subsequently of sealing the container. For these reasons it is conventional practice to provide a pair of endless belts above the level of the conveyor, one belt to each side. The belts advance at the same forward velocity as the conveyor, and grip the containers between them so as to urge the latter forward whilst at the same time automatically providing the required centralisation of the containers and also preventing the latter from toppling either forwards or sideways.
These side belts must engage a portion of each container so shaped as to enable the belts to exert a sufficient frictional force on the container. Most bottles or jars are of circular cross-section in plan (though it should be noted that this invention is not confined to applications in connection with containers of such cross-section). The side belts should engage upon a portion of the container which is cylindrical or nearly cylindrical, or which for some other reason is so shaped in elevation that the belts can satisfactorily grip without any tendency, for example, to slip upwardly or downwardly. Such upward or downward slippage would for example tend to occur if the greater part of the container is in the form of part of a sphere and the side belts are engaged on the spherical surface. It is accordingly necessary, if the capping machine is to be adapted to handle containers of multifarious shapes, to provide means whereby the height at which the side belts are set above the conveyor may be chosen for its suitability for any particular shape of container, i.e. so that the belts will engage that part of the container best suited for the purpose.
Adjustment of side belt height is also necessary in the case, discussed above in another connection, in which batches of containers of different heights (as between one batch and another) are to be handled by the capping machine. Conventionally, this adjustment is achieved by providing three sets of side belt brackets as change parts. The side belts are suitably mounted on these brackets, and each set of the latter is so dimensioned as to determine a different one of three heights of side belt above the conveyor.
Changing the side belt brackets is a fairly major operation, calling for a considerable amount of dismantling, re-assembly, and re-adjustment before the capping machine can be put into productive use again. The higher the speed at which the machine is designed to operate, the more expensive in terms of lost operating time is the period of inaction whilst side belt brackets are changed. In addition, the additional costs of acquiring and storing change parts are a serious disadvantage. These and other well-known disadvantages do of course apply wherever provision of change parts are necessary.
It is however necessary that side belts, at whatever height, should be accurately positioned, both as to the transverse spacing between them and as to their parallelism with respect to the conveyor.
At the sealing station, the cap is secured to the container by sealing means which applies an axial force to the cap (with or without any necessary rotational movement) according to the type of cap being applied.
The sealing means of the capping machine applies downward axial pressure on the cap which has been placed upon the container at the pick-up point, by means of a sealing shoe, which is biassed downwardly by a spring or springs to provide the necessary axial sealing force. The sealing shoe may also be provided with means for heating the shoe and consequently the cap if the latter is of a kind requiring such heating. Underlying the sealing shoe, and in contact with it, is at least one sealing belt in the form of an endless belt, which is driven at a predetermined speed, preferably deriving its motion from the same motor that drives the conveyor and side belts. The sealing belt assists the forward movement of the container, and ensures that the cap remains placed upon the latter until it has been moved axially downwards so that it can no longer be pushed off the container in a direction having a radial component. Where twisting action is also required in order to effect securing of the cap upon the container (as is for example the case with a screw cap or a twist-off cap of the kind which is not adapted to be pushed on to the container by application of a simple axial force), two sealing belts are provided. The two sealing belts are driven at different speeds; and both engage the top of the cap simultaneously. Thus the cap is turned about its axis whilst being pushed down on the container.
Particularly in high-speed operation, it is desirable to ensure very smooth and accurately controlled vertical movement of the sealing shoe, whilst at the same time preventing any sideways or forward movement of the shoe in a horizontal plane.